1. Field of the invention
This invention relates to apparatus and a method for controlling the volumetric flow rate in a conduit in a fluid sample analyzer of the automated type.
2. Prior art
Heretofore, each of a series of fluid samples flowing in a conduit seriatum having been divided into aliquot portions, each aliquot being treated differently for a different constituent of the sample, and subsequently each sample aliquot has been analyzed for the particular constituent in phased relation to every other aliquot, as in Skeggs et al U.S. Pat. No. 3,241, 432. In such an automated analyzer wherein the results of the analyses are displayed in real time, it is important that each aliquot reach analysis at the proper phased interval with reference to every other aliquot, and it has been noted that, on occasion, the various channels in such apparatus will slip out of phase due to such factors as temperature differences, viscosity differences and/or changes in tube diameter for example. In automated fluid sample analyzers proposed since the issuance of the aforementioned Skeggs et al U.S. Patent, it has been proposed, to avoid the problem by utilization of electronic components in electrical circuitry to provide a memory bank in which to store analytical data which may be recovered at intervals for suitable printout of the analytical results. In other words, the analyses are not made in real time. In many instances, the avoidance of this problem has added considerably to the cost of such fluid sample analyzer. It has been proposed to control the sequence of flow in analytical channels by a controller, such as a clock. However, such proposal has not overcome the problems attendant upon proper sequencing with reference to analysis such as discussed above.
In Pelavin U.S. Pat. No. 3,418,053, there is described a technique for detecting a characteristic in a fluid conduit of rate of flow therein, such as by photometric detection of an interface between a liquid and a gas. Such detection has generated a signal which has in some way affected the analytical process, such for example as deactivation of a recorder.
In Bannister et al, U.S. Pat. No. 3,756,459, there is disclosed analysis apparatus for metering a reagent for the periodic phased flow of the reagent in plural conduits from a common pressurized source. A valve controlling flow of a gas into one of the aforementioned conduits is closed by a controller periodically to permit flow of the reagent in the conduit from the pressurized source, flow of reagent in the conduit having previously been precluded by a same pressure of gas downstream in the conduit past the valve. By the same pressure, it is meant pressure the same as the pressure on the source. A photodetector downstream in the conduit detects a liquid-gas interface after commencement of the flow of the reagent and generates a signal to the controller to open the valve which once again stops the flow in the conduit from the source, and accelerates the segment of reagent down the conduit followed by the gas therein flowing past the open valve. No provision is made for proportionately increasing or decreasing the flow rate in response to the signal from the photodetection. The expressed purpose of the apparatus is to time the introduction of a predetermined volume of reagent into a volume of sample which sample volume is predetermined in some other manner.